1. Field of the Invention
The invention relates to a method for actively damping a ship's motion while the ship is sailing by driving at least one first rotatable damping element that extends from the ship's hull, below the water line, on a side of the ship.
The invention also relates to a device for actively damping a ship's motion, comprising at least one first rotatable damping element extending from the ship's hull, below the water line, on a side of the ship, sensor means for sensing the ship's motion and delivering control signals on the basis thereof, driving means for rotatably driving the stabilisation element on the basis of the control signals being delivered for the purpose of damping the ship's motion being sensed.
2. Background Art
Such an active stabilisation system for damping a ship's motion is known, for example from NL patent No. 1023921. In said patent it is proposed to rotate a stabilisation element that projects into the water from the ship's hull below the waterline about its longitudinal axis so as to compensate for the ship's roll while the ship is stationary. The ship is for that purpose fitted with sensor means, for example angle sensors, speed sensors and acceleration sensors, by means of which the angle, the speed or the acceleration of the roll are sensed. Control signals are generated on the basis of the data being obtained, which signals control the rotation of the rotatable stabilisation element as regards the direction of rotation and the speed of rotation of the stabilisation element as well as the movement of the stabilisation element relative to the ship.
Under the influence of the rotational movement of the stabilisation element and the water flowing past as a result of the stabilisation element moving relative to the stationary ship, a correction force perpendicular to the direction of rotation and the ship's direction of movement is generated. This physical phenomenon is also referred to as the Magnus effect, on the basis of which the correction force is used for opposing the ship's roll.
A drawback of the stabilisation system according to said Dutch patent is that it can only be used while the ship is stationary. If such an active stabilisation system is used with ships while sailing, the system will be opposed by the increased frictional resistance on the one hand and by the mass inertia of the system, because the direction of rotation of the stabilisation elements needs to be reversed all the time, on the other hand.